Non-nutritive food additives and antibiotics are entering the food chain in ever increasing amounts. Consequently, there is increased public health concerns over the effects these compounds may have on the human intestinal microflora. Shifts in populations of intestinal bacteria can result in colonic disorders such diarrhea, flatulence and decreased resistance to intestinal pathogens. Whereas there are several ways to monitor the effects of food additives on the flora's metabolic activity, there is still no feasible way to screen for changes in bacterial populations. Classical taxonomic techniques involve costly culturing which cannot be adapted to large numbers of samples. However, analysis of cellular fatty acids (CFAs) by gas chromatography, which is used to rapidly identify bacteria, can now be adapted using new statistical methods to determine the relatedness among bacterial populations. The studies proposed herein will determine the feasibility of using CFA analysis to establish "fingerprints" for bacterial populations in rodents and to resolve shifts in bacterial populations upon dietary intervention. As a rapid, and highly resolving technique, CFA fingerprinting of intestinal contents could become a preferred means by which food or pharmaceutical companies may monitor the effects of compounds in feeding trials during product development.